The 6' 3" Needham, Mass., native has excelled at sports since he was a kid. At 13, he hit a hole in one on the golf course, and he broke 11 school records while playing wide receiver for Yale University. He's also a former academic All-American, who was called "The Big Nerd" by his Yale friends, according to a 2004 article in the San Francisco Chronicle.

"He is very smart," says the NFL source, "and he is one of the most down-to-earth athletes I know."

And that could come in handy when dating a Hollywood starlet.

Simpson began dating Johnson in May after friends introduced them. He's currently separated from his wife, Keri, who filed for divorce earlier this year.

"He is the polar opposite of what you think of when you say 'player,' " says the NFL source. "When I met him, he was driving a Prius when other athletes were driving gas-guzzling cars."